There are various methods for ascertaining the color discrimination of human beings. One known method is the color spot or color arrangement test. T. Schneider describes such a method in an article entitled "Einfuhrung in die Farbsinnprufung," (Introduction to Color Discrimination Testing) Z. Prakt. Augenheilkd (Journal for Practical Ophthamology), vol. 10, pp. 29-35 (1989). The principle of this test is to present the subject with a series of various color spots and ask the subject to arrange the spots in the correct sequence in accordance with the gradual color change. For those whose color vision is impeded, mistakes that are more or less characteristic for the particular disorder occur.
The best known example of this type of color vision test is the Farnsworth-Munsell 100-Hue Test which has 85 movable and 8 fixed color caps each with a diameter of 5 mm. Taken together, these 93 caps form a sample of the natural color spectrum and of the range of purple colors. The caps are distributed among four trays. When placed one abutting the other using the criterion that the most similar colors are arranged one after the other, the caps produce a closed color circle. Each cap and hence each color spot is assigned a number which makes it possible to calculate how many partial mistakes are made and to calculate the total number of mistakes. The total number of mistakes, particularly in inherited color vision disorders, is a good parameter for monitoring the course of any disorder.
Ascertaining the number of mistakes is relatively time-consuming, however, and involves a certain likelihood of error. Attempts have been made to reduce the effort by using suitable computer programs but the sequence in which the subject places the cap cannot be used to calculate the numbers of mistakes until after it has been entered manually into the computer. Although this does accomplish a certain time savings in calculation, nevertheless the input itself is time-consuming as well, and above all requires high concentration if data entry errors are to be kept low.
Other methods utilize automated systems. G. B. Donaldson describes in article entitled "Instrumentation for the Farnsworth-Munsell 100-Hue Test," J. Opt. Soc. Am., vol. 67, pp. 248-9 (1977), an apparatus for automated ascertainment of the sequence of color spot disks. Switch elements in the form of one resistor and one Zener diode are each mounted and connected in parallel in the caps that contain the color disks. By suitable combinations of these switch elements, it is possible to encode the color disks suitably and by using electrical plug connections mounted on the underside of the color caps the sequence in which the color disks are placed can be ascertained. Several disadvantages are associated with this method. In order to perform the method, the subject (patient) needs to rearrange the color caps, which are usually in random order, in front of the subject (patient) on a table top. In the normal Farnsworth-Munsell 100-Hue Test this does not create a problem since the underside of each cap is flat. In the automated version described by Donaldson, simply placing the randomly ordered color caps on the table top is not possible because the color caps do not have a flat bottom surface, and thus the individual color caps can no longer be placed on the table in front of the subject stably with the colored surface facing upward. Instead, because the color caps have a plug mounted on their underside the color caps rest somewhat like a toy top on the flat surface of the table and the colored surfaces of the caps are oriented in an arbitrary direction instead of facing upward toward the subject. This hinders the subject's ability to make a color choice. Also, the color spot disks should be displaceable in the arrangement direction so that if the subject wants to place one more color caps between two or more color caps that have already been put in place, the subject can create a suitable space by shifting the already-placed caps. This is not possible in Donaldson's automated method because all of the caps that are already arranged have to be unplugged from the plug connections and plugged into the positions corresponding to the necessary shifting. Only then can the subject plug the desired cap into the position that has now been made available. If the subject, once he has looked at the partial color sequence thus arranged decides that the cap now placed in between other color caps still does not fit this location in terms of its color, which is often the case, then the subject has to undo all the unplugging and plugging maneuvers he has already performed. In addition, the plug connection is not only an electrical part but also a mechanical part and is thus vulnerable to wear. Also the electrical components of the color caps have a relatively limited service life. If the Zener diode in the interior of the color cap should break, for instance, it must be replaced which would involve a not inconsiderable amount of effort.
To circumvent at least some of these disadvantages, PCT Application No. WO 88/0317A1 published Jun. 2, 1988 describes an apparatus for automated determination of the color sequence arranged in color arrangement tests. More particularly, a bar code-type reader system is employed. A bar code, preferably formed by concentric rings, is placed on each of the color caps so that each color cap, regardless of its orientation can be identified using a scanner. There are several disadvantages associated with this method. Because a suitable scanner must scan across the color caps, a movable mechanical device is required. This introduces a certain vulnerability in the system to malfunction and a certain need for repair and maintenance which increases with the more tests per unit of time that are performed. Also, the mechanical system must be of high quality and is therefore expensive. In addition, bar code systems are not immune from error, not every attempt at reading is successful. Also, the scanner device can become dirty which leads to an increased need for maintenance.
Thus it is desirable to provide an apparatus for the automated determination of the sequence of color caps in a color spot or color arrangement test that does not have the disadvantages listed above.